On Mon, Oct 04, 2021 at 11:42:23PM +0100, Matthew Wilcox (Oracle) wrote:
> Move the compound page overrun detection out of
> CONFIG_HARDENED_USERCOPY_PAGESPAN so it's enabled for more people.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> mm/usercopy.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/mm/usercopy.c b/mm/usercopy.c
> index 7bfc4f9ed1e4..e395462961d5 100644
> --- a/mm/usercopy.c
> +++ b/mm/usercopy.c
> @@ -194,11 +194,6 @@ static inline void check_page_span(const void *ptr, unsigned long n,
> ((unsigned long)end & (unsigned long)PAGE_MASK)))
> return;
>
> - /* Allow if fully inside the same compound (__GFP_COMP) page. */
> - endpage = virt_to_head_page(end);
> - if (likely(endpage == page))
> - return;
> -
> /*
> * Reject if range is entirely either Reserved (i.e. special or
> * device memory), or CMA. Otherwise, reject since the object spans
> @@ -250,6 +245,10 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
> if (PageSlab(page)) {
> /* Check slab allocator for flags and size. */
> __check_heap_object(ptr, n, page, to_user);
> + } else if (PageHead(page)) {
> + /* A compound allocation */
> + if (ptr + n > page_address(page) + page_size(page))
> + usercopy_abort("page alloc", NULL, to_user, 0, n);
"0" could be "ptr - page_address(page)", I think? With that:
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
-Kees
> } else {
> /* Verify object does not incorrectly span multiple pages. */
> check_page_span(ptr, n, page, to_user);
> --
> 2.32.0
>
--
Kees Cook
